There has long been a desire to develop a universal system for detecting molecular species found in biological fluids or synthetic chemical environments. Currently there are a variety of specialized instruments, all of which are large, cumbersome, relatively slow, and expensive to operate, requiring a highly skilled staff.
Two of the most commonly used techniques for measuring the presence and quantity of an analyte in a test sample are ELISA and RIA.
There are many different types of ELISA procedures. The most general format consists of depositing the antigen of choice at a specific concentration in a 96 well plastic plate. The antigen solution is incubated in the plate for one hour before excess antigen is washed out. The plate is then coated with antigen, but the remaining electrostatic charges on the plate must be blocked with a protein buffer for another hour so that test proteins and reagents, which are added later, do not non-specifically bind to the plate. The plate is washed once again before adding the test samples and incubated for another hour. This cycle of washing is repeated and an enzyme labeled anti-ligand is added and incubated for one more hour. Once this last incubation is finished, the plate is thoroughly washed and the enzyme substrate is added. If enzyme is present, the substrate will be converted to product. A colorimetric change occurs which is measured by suitable instrumentation. The data are then expressed on a computer screen or printed by a printer. In some ELISAs, the sample preparation may take as much as an entire day before a reading can be taken.
An RIA is usually more sensitive than an ELISA. The probe used is radioactive and requires special disposal facilities. The sequence steps of the assay are the same as the ELISA, but the probe binds directly to the target molecule without enzymatic conversion of a substrate to a colored product. In a competitive RIA, the radioactive probe and the non-radioactive molecule of interest found in the test sample compete for a common binding site. The gamma and beta radioactive counters used to detect the radiation are large table top or floor model instruments that print out data.
Other techniques and complementary instruments are used for detecting biomolecules, including PANDEX, TDX, HPLC (high performance liquid chromatography), PHAST, GC (gas chromatography), FACS, and others.
Unfortunately, none of the above assays is capable of providing a rapid, reliable identification of fish or other animals rapidly and accurately as to their age, origin, and any experimental protocols to which they have been subjected. Presently available methods are cumbersome (e.g., wire tags), lethal (e.g., otolith marks and wire tags), expensive, and technically demanding (e.g., rare earth metals and genetic testing). All of these methods are time consuming, and most are too large to use with very small fish.